Course on Computer Communication and Networks. Lecture 16 Synthesis, Summary/flashback and Projection (related topics continuation of study)

Transcription

1 Course on Computer Communication and Networks Lecture 16 Synthesis, Summary/flashback and Projection (related topics continuation of study) EDA344/DIT 423, CTH/GU Based on the book Computer Networking: A Top Down Approach, Jim Kurose, Keith Ross, Addison-Wesley. Marina Papatriantafilou Summary flashback and projection 1

2 Important for the exam When/where: wednesday March 14, , SB-building You may have with you: English-X dictionary no calculators, PDAs, etc (if/where numbers matter, do rounding) Grading 30-40, 41-50, (out of 60)= 3, 4, 5 (CTH) 30-44, (out of 60) = G, VG (GU) To think during summary-study Have overview, critical eye; explain; ask yourselves: why is this so? / how does it work (or not work)? Marina Papatriantafilou Summary flashback and projection 2

3 Roadmap Synthesis: Putting lots-of-what-we-learned together: a day in the life of a web request goal: identify, review protocols (at all layers) involved in seemingly simple scenario: Scenario requesting www page: student attaches laptop to campus network, requests/receives Marina Papatriantafilou Summary flashback and projection 3

4 A day in the life. : scenario browser Comcast network /13 DNS server school network /24 web page web server Google s network /19 Marina Papatriantafilou Summary flashback and projection 4

5 A day in the life connecting to the Internet UDP IP Eth Phy connecting laptop needs to get its own IP address: use UDP IP Eth Phy router (runs ) request encapsulated in UDP, encapsulated in IP, encapsulated in Ethernet Ethernet frame broadcast (dest: FFFFFFFFFFFF) on LAN, received at router running server Ethernet demux ed to IP demux ed to UDP demux ed to Marina Papatriantafilou Summary flashback and projection 5

6 A day in the life connecting to the Internet UDP IP Eth Phy server formulates ACK containing client s IP address (and also IP address of first-hop router for client, name & IP address of DNS server) UDP IP Eth Phy router (runs ) frame forwarded (switch learning) through LAN, demultiplexing at client client receives ACK reply Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router Marina Papatriantafilou Summary flashback and projection 6

7 A day in the life ARP (before DNS, before HTTP) DNS DNS DNS ARP query DNS UDP IP Eth Phy ARP ARP reply ARP Eth Phy before sending HTTP request, need IP address of DNS DNS query created, encapsulated in UDP, encapsulated in IP, encasulated in Eth. In order to send frame to router, need MAC address of router interface: ARP ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface client now knows MAC address of first hop router, so can now send frame containing DNS query Marina Papatriantafilou Summary flashback and projection 7

8 A day in the life using DNS DNS DNS DNS DNS DNS DNS UDP IP Eth Phy DNS DNS DNS DNS DNS UDP IP Eth Phy Comcast network /13 DNS server IP datagram containing DNS query forwarded via LAN switch from client to 1 st hop router IP datagram forwarded from campus network to destination (DNS-server) network, routed (tables created by OSPF and BGP routing protocols) to DNS server demux ed to DNS server DNS server replies to client with IP address of Marina Papatriantafilou Summary flashback and projection 8

9 A day in the life TCP connection carrying HTTP HTTP SYNACK SYNACK SYNACK HTTP TCP IP Eth Phy SYNACK SYNACK SYNACK TCP IP Eth Phy to send HTTP request, client first opens TCP socket to web server TCP SYN segment (step 1 in 3- way handshake) inter-domain routed to web server web server responds with TCP SYNACK web server TCP connection established! Marina Papatriantafilou Summary flashback and projection 9

10 A day in the life HTTP request/reply HTTP HTTP HTTP HTTP HTTP HTTP TCP IP Eth Phy web page finally (!!!) displayed HTTP HTTP HTTP HTTP HTTP TCP IP Eth Phy HTTP request sent into TCP socket IP datagram containing HTTP request routed to web server responds with HTTP reply (containing web page) web server IP datgram containing HTTP reply routed back to client Marina Papatriantafilou Summary flashback and projection 10

11 Roadmap Synthesis: a day in the life of a web request Putting lots-of-what-we-learned together: synthesis! goal: identify, review protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus network, requests/receives Highlights.. Marina Papatriantafilou Summary flashback and projection 11

12 Principles, Organisation Network Problems Continuously evolving applications, mobility, performance, security,, serving different types of traffic, connecting transparently different networks, routing, congestion control, to shared (broadcast) transmission medium producer-consumer problems, flow and error control Layering : principle, why Marina Papatriantafilou Summary flashback and projection 12

13 Highlights Routing + mobility + SDN multiple protocols (wired, wireless) TCP/IP, LAN evolving protocol stack (http2, quic, ) Evolving types of applications: media, CDN, IoT network security issues delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary flashback and projection 13

14 Types of delay; performance Propagation, transmission, queueing, processing Throughput (effective bandwidth), utilization -- efficiency Packet-switching: impact of store&forward, pipelines, spacetime diagrams Sliding windows performance Relation between delays-losses initiate TCP connection request object RTT first window = S/R second window = 2S/R third window = 4S/R fourth window = 8S/R object delivered complete transmission A transmission propagation time at client time at server B nodal processing queuing Marina Papatriantafilou Summary flashback and projection 14

15 Reliable data transfer Guaranteed, in-order, correct delivery: stop&wait sliding windows sequence numbers window sizes dynamic windows (TCP) flow control Error detection: checksums Error control: go-back-n, selective repeat, FEC methods Marina Papatriantafilou Summary flashback and projection 15

16 Datagram vs VC endto-end comm. Conceptual differences Congestion Control RT traffic/streaming Marina Papatriantafilou Summary flashback and projection 16

17 Congestion control (CC) why, how congestion occurs CC in TCP and performance; implied weaknesses CC in other ways, e.g. VC-based networks Real-time (RT)-traffic resource reservation: traffic shaping and policing rate-based Marina Papatriantafilou Summary flashback and projection 17

18 Highlights Routing + mobility + SDN multiple protocols (wired, wireless) TCP/IP, LAN evolving protocol stack (http2, quic, ) Evolving types of applications: media, CDN, IoT network security issues delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary flashback and projection 18

19 Evolving types of applications ++ P2P/streaming applications-infrastructure (application-layer networking) Varying approaches for MM apps, besides conceptual, VC-related Application-level solutions (playout delay, forward-error-control, caching- CDN, FEC) Marina Papatriantafilou Summary flashback and projection 19

20 Routing + mobility + SDN Routing algorithms, protocols Forwarding in routers Resource, policy issues Data plane and control plane in SDN Addressing mobility, tunneling A B 2 D C 1 E 5 2 F Mobile Switching Center Mobile Switching Center Public telephone network, and Internet Marina Papatriantafilou Summary flashback and projection 20

21 Medium : multiple methods Strategies: (functionality, appropriateness) Contention-based (random ), wired/wireless: Aloha, CSMA(CD/CA) Collision-free: Channel partitioning: TDMA, FDMA, CDMA Taking turns: e.g. tokens, reservation-based A B C A s signal strength C s signal strength space Marina Papatriantafilou Summary flashback and projection 21

22 Security issues C, I, A and methods to achieve them The language of cryptography Message integrity, signatures Instantiation in Internet: SSL, IPsec Firewalls Alice channel data, control messages Bob data secure sender s secure receiver data Trudy Marina Papatriantafilou Summary flashback and projection 22

23 Highlights Routing + mobility + SDN multiple protocols (wired, wireless) TCP/IP, LAN evolving protocol stack (http2, quic, ) Evolving types of applications: media, CDN, IoT network security issues delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary flashback and projection 23

24 TCP/IP protocol stack, applications, evolution Instantiation of network solutions, advantages, limitations, updates http, DNS, SMTP, TCP. UDP, IP, routing protocols LAN Protocol Examples: wired, wireless: Ethernet, 802.xy, GSM: Connecting devices: functionalities and differences (Hubs, switches) Algorithms for switch- routing : learning& forwarding of packets ARP New types of applications and how they function in the Internet Changing NW-edge: Intserv/diffserv, http2, quic, IoT-related protocols switch Marina Papatriantafilou Summary flashback and projection 24

25 Roadmap Synthesis: a day in the life of a web request Putting lots-of-what-we-learned together: synthesis! goal: identify, review protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus network, requests/receives Highlights Some questions asked by you Marina Papatriantafilou Summary flashback and projection 25

26 some questions asked by you: Marina Papatriantafilou Summary flashback and projection 1. How can we have reliable data transfer on top of UDP Implementation at applayer 2. RDT with only NACK possible?: no-lossy channel Timeout => ok, msg received lossy channel: Cannot tell difference between late or lost. 3. Working with time-space diagrams Eg. what is a full utilization window? first packet bit transmitted, t = 0 last bit transmitted, t = L / R RTT ACK arrives, send next packet, t = RTT + L / R sender receiver first packet bit arrives last packet bit arrives, send ACK last bit of 2 nd packet arrives, send ACK last bit of 3 rd packet arrives, send ACK E.g. for 100% utilization, calculate how many packets can fill in RTT + L / R, ie (RTT + L / R)/ (L / R) 26

27 Roadmap Synthesis: a day in the life of a web request Putting lots-of-what-we-learned together: synthesis! goal: identify, review protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus network, requests/receives Highlights Some questions asked by you Reflections, prespectives. Marina Papatriantafilou Summary flashback and projection 27

28 The Internet: virtualizing networks Internetwork layer (IP): addressing: internetwork appears as single, uniform entity, despite underlying local network heterogeneity network of networks Gateway: embed internetwork packets in local packet format route (at internetwork level) to next gateway gateway ARPAnet satellite net Marina Papatriantafilou Summary flashback and projection 5-28

29 Marina Papatriantafilou Summary flashback and projection Internet structure: network of networks and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users net net net ISP A net net net net net Content provider network IXP ISP B net net ISP B net net net regional net net net net

30 Internet structure: network of networks Tier 1 ISP Tier 1 ISP Google IXP Regional ISP IXP Regional ISP IXP ISP ISP ISP ISP ISP ISP ISP ISP Marina Papatriantafilou Summary flashback and projection Introduction 1-30

31 Data center networks 10 s to 100 s of thousands of hosts, often closely coupled, in close proximity: e-business (e.g. Amazon) content-servers (e.g., YouTube, Akamai, Apple, Microsoft) search engines, data mining (e.g., Google) challenges: multiple applications, each serving massive numbers of clients managing/balancing load, networking, data bottlenecks Inside a 40-ft Microsoft container, Chicago data center Marina Papatriantafilou Summary flashback and projection 5-31

32 Data center networks load balancer: application-layer routing directs client requests (workload) within data center Internet rich interconnection among switches, racks: increased throughput between racks (multiple routing paths possible) increased reliability via redundancy Distributed systems & networks working together (guest lectures relevance) Load balancer B Access router Border router Load balancer Tier-1 switches A C Tier-2 switches TOR switches Server racks Marina Papatriantafilou Summary flashback and projection 32

33 Thank you! Synthesis: a day in the life of a web request Putting lots-of-what-we-learned together: synthesis! goal: identify, review protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus network, requests/receives Highlights Some questions asked by you Reflections, prespectives Recall, important for the exam: When/where: wednesday March 14, , SB Good luck with all your efforts!!! You may have with you: English-X dictionary no calculators, PDAs, etc (if/where numbers matter, do rounding) To think during last, summary-study Overview; critical eye; explain; ask yourselves: why is this so? / How does it work? If you hear a voice within you say you cannot paint, then by all means paint, and that voice will be silenced. Vincent Van Gogh Marina Papatriantafilou Summary flashback and projection 33